On Fri, Jun 04, 2010 at 08:46:49PM +0930, Rusty Russell wrote:> On Fri, 4 Jun 2010 08:05:43 pm Michael S. Tsirkin wrote:> > On Fri, Jun 04, 2010 at 12:04:57PM +0930, Rusty Russell wrote:> > > On Wed, 2 Jun 2010 12:17:12 am Michael S. Tsirkin wrote:> > > > This adds an (unused) option to put available ring before control (avail> > > > index, flags), and adds padding between index and flags. This avoids> > > > cache line sharing between control and ring, and also makes it possible> > > > to extend avail control without incurring extra cache misses.> > > > > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>> > > > > > No no no no. 254? You're trying to Morton me![1]> > > > Hmm, I wonder what will we do if we want a 3rd field on> > a separate chacheline. But ok.> > > > > How's this (untested):> > > > I think we also want to put flags there as well,> > they are used on interrupt path, together with last used index.> > I'm uncomfortable with moving a field.> > We haven't done that before and I wonder what will break with old code.

With e.g. my patch, We only do this conditionally when bit is negotitated.

> Should we instead just abandon the flags field and use last_used only?> Or, more radically, put flags == last_used when the feature is on?> > Thoughts?> Rusty.

Hmm, e.g. with TX and virtio net, we almost never want interrupts,whatever the index value.